Carbon dioxide (CO2) has been identified as the main source of greenhouse gas contributing to the climate changes. Therefore, capturing and sequestering CO2 has been recognized as a potential solution to climate changes caused by greenhouse gases. Billions of tons of CO2 are annually emitted by fuel combustion processes, where the vast majority is emitted from power plants. Post-combustion CO2 mitigation is an attractive option for reducing the impact of greenhouse gasses that emitted to the atmosphere. A current method for capturing CO2 involves chemical absorption in an amine solution. This process is costly and requires large amounts of time and space.
Efficient separation technologies are required to remove carbon dioxide from flue gas streams of power plants especially coal burning power plants. Membrane-based processes for gas separation are attractive because they are (i) highly energy-efficient, (ii) simple to operate and maintain, (iii) compact and modular, allowing for easy retrofit to existing power plants. One difficulty for the use of membrane technology is that flue gas, especially from coal burning power plants, contains metal oxides which are acidic in nature and also SOx and NOx gases which could attack the membrane and deteriorate its performance.
US 20080078290 describes a gas separation membrane formed from a blend of polyvinylalcohol and polyvinylamine. Although these membranes showed separation properties, but are not fluorinated, as a result, they would be susceptible to acid attack results in performance deterioration.
Polyvinylidene fluoride (PVDF) membranes are being used in microfiltration and ultrafiltration applications, and have been described in US patents such as U.S. Pat. Nos. 6,013,688, 6,110,309, and US 2008/0220274.
U.S. Pat. No. 5,490,931 describes 2-layer hollow fiber fluid separation membranes having a fluoropolymer layer, said fluoropolymer having a nitrogen-containing backbone. U.S. Pat. No. 7,811,359 describes a multi-layer membrane for the separation of carbon dioxide, in which an expanded polytetrafluoroethylene layer is used as a support layer for a polyorganosiloxane active layer.
US 20090301307 describes a gas separation membrane that comprises a porous support membrane and a gas-separating thin film that comprises a gas-separating resin as a main component. The polymeric microporous membrane contains one or two types of ultrahigh molecular weight polyethylene and polypropylene as porous support. The gas-separating membrane resin is made of a copolymer of perfluoro-2,2-dimethyl-1,3-dioxol and tetrafluoroethylene (TFE). pTFE is not a polar material, and therefore its selectivity is diminished compared to PVDF or ETFE of the present invention.
There remains a need to develop separating membranes or films that not only do not suffer from the problems highlighted above, but further possess excellent gas selectivity and high permeance for targeted gas.
Surprisingly, a media for gas separation has now been developed, formed from polyethylene tetrafluoro ethylene (ETFE)-based and/or polyvinylidene fluoride (PVDF)-based polymers, that exhibits excellent separation properties, excellent mechanical properties, and withstands acid, NOx and SOx attacks. The media, especially in the form of a film or membrane does not suffer from performance deterioration after being exposed to NOx and SOx for long period of time.